1. Field of the Invention
This invention concerns an oxygen generating system and, more specifically, it relates to a portable oxygen generating system for continuously generating gaseous oxygen by the catalytic decomposition of aqueous hydrogen peroxide.
2. Description of the Prior Art
Oxygen gas has been utilized broadly for various applications such as medical, industrial and experimental uses, and most of oxygen generating apparatus in the prior art are voluminous and heavy due to the use of high pressure gas cylinders as the oxygen supply source. Although the handling of the oxygen gas cylinder is inconvenient and improvement has been demanded therefor, no suitable means have yet been developed.
By the way, as ceramics and various types of high melting alloys have been utilized in various fields along with the development of such new materials in recent years, compact heat processing means capable of simply melting or welding these materials at high temperature have been required.
As such heat processing apparatus, compact and weight-reduced combustion apparatus using liquefied gas as a heat catalyst source have already been put to practical use, such as a gas soldering iron, gas torch or hot blow developed by the present inventor. Accordingly, if any compact oxygen generating system is combined with such apparatus, melting or welding fabrication to dental materials, ornamental alloys, ceramics or the like can be applied with ease by the high temperature of so-called oxygen added combustion flames.
However, compact and lightweight oxygen generating systems that can supply oxygen gas for a long time are not yet known or used. As one of the means for reducing the size and the weight of the oxygen generating system, it will be effective to replace the high pressure oxygen gas cylinder as described above with a source of an aqueous hydrogen peroxide which is available readily, can be handled with ease and produce a great amount of oxygen per unit volume and decompose the same with the aid of a catalyst.
Japanese Utility Model Publication No. 26445/1980 discloses an oxygen gas generating system adapted to catalytically decompose aqueous hydrogen peroxide by using a manganese compound as a catalyst and utilize the thus obtained oxygen gas for life support systems in hospitals, etc.
However, since the decomposing reaction of the aqueous hydrogen peroxide with manganese dioxide or the like proceeds at an explosively high rate if the concentration of hydrogen peroxide exceeds about 5 w/w %, the concentration of aqueous hydrogen peroxide is usually limited to about 3 w/w %. However, if the volume (and weight) of a reservoir for aqueous hydrogen peroxide is intended to be decreased with the practical demand of reducing the entire size of the oxygen generating system so that the system can be portable, hydrogen peroxide at such a low concentration is rapidly consumed and the reservoir has to be replaced frequently, which is not practical at all.
While on the other hand, there has been known a platinum type catalyst capable of stably decomposing aqueous hydrogen peroxide at a high concentration (for example, from 30 to 60 w/w %) as disclosed in Japanese Patent Publication No. 42155/1977. However, the abovementioned catalyst has been found not satisfactory for use in actual oxygen generating system with the purpose as described above.
At first, for completely decomposing the aqueous hydrogen peroxide of a relatively limited flow rate and generating the oxygen gas efficiently for a long period of time, it is necessary that the reaction area of the catalyst per unit volume is increased as much as possible and also important that the catalyst is free from destruction and detachment from the support due to defoliation during use. However, no effective practical means are disclosed in this regard. For instance, if a support made of alumina or silica gel with a usual pore size about from 5 .mu.m to 50 .mu.m is used as in the conventional supported catalyst, the aqueous hydrogen peroxide as the reactant can not readily penetrate to the inside of the support.
In addition, since the gas pressure inside the pores is increased upon decomposing reaction, penetration of the reaction solution to the pores is further hindered. Further, most of the catalyst component is carried only near the surface of the support and, after all, the reaction is carried out only near the surface thereof. Further, the catalyst layer on the support tends to suffer from destruction and detachment with the increase of the gas pressure inside the support and to be washed out by the aqueous hydrogen peroxide. This limits the catalyst life extremely.
Furthermore, since the decomposition of aqueous hydrogen peroxide is an exothermic reaction as shown by the scheme: EQU H.sub.2 O.sub.2 .fwdarw.H.sub.2 O+1/2O.sub.2 EQU .DELTA.H29.8=-23.47 Kcalg.sup.-1 mol.sup.-1
it is desirable to maintain the reaction temperature as high as possible for promoting the decomposing reaction. Therefore, it is preferred to maintain the temperature of the catalyst to a predetermined temperature higher than the ambient temperature. However, the customary temperature control has been done in the direction of cooling rather than heating the reaction zone in order to avoid the uncontrollable and explosive decomposing reaction of aqueous hydrogen peroxide. Thus, temperature increase in the decomposing hydrogen peroxide reaction has been considered undesirable and not suggested at all in the prior art including the reference as described above.
Anyway, if it is intended to decompose aqueous hydrogen peroxide at an increased temperature, it would be indispensable for always controlling the flow rate of hydrogen peroxide to be supplied extremely strictly for the safe and stable decomposition thereof.
In the prior art, a system of controlling the flow rate of hydrogen peroxide by adjusting the opening degree of a valve for supplying aqueous hydrogen peroxide depending on the pressure of the generated oxygen gas by means of a link mechanism or the like has been proposed as disclosed, for example, in Japanese Patent Publication No. 49843/1981 (although the concentration of aqueous hydrogen peroxide is not high and the temperature is kept low in this case). However, in the proposed system of converting the gas pressure into mechanical displacement and transmitting the displacement by means of the link, it is difficult to rapidly respond to the change in the reaction rate and failures are liable to be caused due to the corrosion or abrasion in the actuation mechanism or the failure in the operation of the valve.
In summary, an oxygen generating system which is compact and of a reduced weight, as well as capable of supplying oxygen gas at a sufficient flow rate stably for a long period of time has to satisfy the requirements that aqueous hydrogen peroxide at a high concentration (at least greater than 5 w/w %) can be used as an oxygen generation source, the catalyst and that the catalyst support has a long service life, can completely and stably decompose the aqueous hydrogen peroxide and perform the decomposition of the aqueous hydrogen peroxide at a temperature as high as possible and under safety control.
However, oxygen generating systems capable of satisfying such requirements have not yet been known at all in the prior art including the literatures as cited above.